Ottoman rule ended with World War I, and Iraq came to be administered by the British Empire as Mandatory Iraq until the establishment of the Kingdom of Iraq in 1933. A republic was established in 1958 following a coup d'état. It was controlled by Saddam Hussein from 1979 to 2003, into which period falls the Iran–Iraq War and the Gulf War. Saddam Hussein was deposed following the 2003 US-led invasion of the country. Following the invasion, the situation deteriorated to the extent that in 2006–07, Iraq was on the brink of civil war. However, conditions improved following a surge in U.S. troops in 2007–08, and the war was declared formally over in December 2011, with the U.S. troops leaving the country.

During 1957–1961 Shanidar Cave was excavated by Ralph Solecki and his team from Columbia University, and nine skeletons of Neanderthal man of varying ages and states of preservation and completeness (labelled Shanidar I – IX) were discovered dating from 60–80,000 years BP. A tenth individual was recently discovered by M. Zeder during examination of a faunal assemblage from the site at the Smithsonian Institution. The remains seemed to Zeder to suggest that Neandertals had funeral ceremonies, burying their dead with flowers (although the flowers are now thought to be a modern contaminant), and that they took care of injured and elderly individuals.

Mesopotamia is the site of the earliest developments of the Neolithic Revolution from around 10,000 BC. It has been identified as having "inspired some of the most important developments in human history including the invention of the wheel, the planting of the first cereal crops and the development of cursive script, Mathematics, Astronomy and Agriculture."[7]

Sumer was a civilization and historical region in southern Iraq. It is the earliest known civilization in the world, making Iraq one of the Cradles of Civilization. The Sumerian civilization spanned over 3000 years[8] and began with the first settlement of Eridu in the Ubaid period (mid-6th millennium BC) through the Uruk period (4th millennium BC) and the Early Dynastic periods (3rd millennium BC) until the rise of Assyria and Babylonia in the late 3rd and early 2nd millennium BC respectively.

The Ubaid period marks the Pottery Neolithic to Chalcolithic phase in Mesopotamia, which represents the earliest settlement on the alluvial plain in the south. Early urbanization begins with the Ubaid period, around 5300 BC. The Ubaid culture gives way to the Uruk period from c. 4000 BC. The invention of the wheel and the beginning of the Chalcolithic period fall into the Ubaid period. The Sumerian historical record remains obscure until the Early Dynastic period, when a now deciphered syllabary writing system was developed, which has allowed archaeologists to read contemporary records and inscriptions.

The north of Mesopotamia had become the Akkadian speaking state of Assyria by the late 25th century BC. Along with the rest of Mesopotamia it was ruled by the Akkadian kings from the late 24th to mid 22nd centuries BC, after which it once again became independent.[9]

Assyria was a SemiticAkkadian kingdom in what is now Northern Iraq, extant as a nation state from the late 25th or early–24th century BC to 605 BC. After this it survived as a geo-political entity until the 7th century.[11] centred on the Upper Tigris river, in northern Mesopotamia (present day northern Iraq), that came to rule regional empires a number of times through history. It was named for its original capital, the ancient city of Assur (Akkadian: 𒀸𒋗𒁺 𐎹Aššūrāyu; Aramaic: אתורAṯur; Hebrew: אַשּׁוּרAššûr; Arabic: آشورĀšūr).

Of the early history of the kingdom of Assyria, little is positively known. In the Assyrian King List, the earliest king recorded was Tudiya. He was a contemporary of Ibrium of Ebla who appears to have lived in the late 25th or early 24th century BC, according to the king list. The foundation of the first true urbanised Assyrian monarchy was traditionally ascribed to Ushpia a contemporary of Ishbi-Erra of Isin and Naplanum of Larsa.[12] c. 2030 BC. Assyria had a period of empire from the 19th to 18th centuries BC. From the 14th to 11th centuries BC Assyria once more became a major power with the rise of the Middle Assyrian Empire which dominated the whole of Mesopotamia and much of the Near East and Anatolia. After an interregnum of a hundred or so years, Assyria began to expand once more with the rise of the Neo Assyrian Empire.

Babylonia was a state in central and southern Iraq with Babylon as its capital. It was founded as an independent state by an Amorite king named Sumuabum in 1894 BC.[11] During the 3rd millennium BCE, there developed a very intimate cultural symbiosis between the Sumerians and the Akkadians, which included widespread bilingualism.[16] The influence of Sumerian on Akkadian (and vice versa) is evident in all areas, from lexical borrowing on a massive scale, to syntactic, morphological, and phonological convergence.[16] This has prompted scholars to refer to Sumerian and Akkadian in the 3rd millennium BC as a sprachbund.[16]

Akkadian gradually replaced Sumerian as the spoken language of Mesopotamia somewhere around the turn of the 3rd and the 2nd millennium BCE (the exact dating being a matter of debate),[17] but Sumerian continued to be used as a sacred, ceremonial, literary and scientific language in Mesopotamia until the 1st century CE.

Babylonia emerged from the Amorite dynasties (c. 1900 BC) when Hammurabi (c. 1792–1750 BC), unified the territories of the former kingdoms of Sumer and Akkad. The Babylonian (and Assyrian) culture was a synthesis of Akkadian and Sumerian culture. Babylonians spoke the Akkadian language, and retained the Sumerian language for religious use, which by Hammurabi's time was declining as a spoken language. The rulers of Babylonia carried the title "King of Sumer and Akkad".

The earliest mention of the city of Babylon can be found in a tablet from the reign of Sargon of Akkad, dating back to the 24th century BC. Following the collapse of the Ur-III dynasty at the hands of the Elamites (2002 BC traditional, 1940 BC short), the Amorites gained control over most of Mesopotamia, where they formed a series of small kingdoms. During the 1st centuries of what is called the "Amorite period", the most powerful city states were Isin and Larsa, although Shamshi-Adad I came close to uniting the more northern regions around Assur and Mari. One of these Amorite dynasties was established in the city-state of Babylon, which would ultimately take over the others and form the first Babylonian empire, during what is also called the Old Babylonian Period.

Eventually, during the 9th century BC, one of the most powerful tribes outside Babylon, the SemiticChaldeans (Latin Chaldaeus, Greek Khaldaios, Assyrian Kaldu), gained prominence in the far south east of Mesopotamia, and along with the Elamites made a number of failed attempts to loosen the Assyrian grip on Babylon.

In 620 BC, the Chaldeans helped Nabopolassar to take power in Babylonia. At that time, Assyria riven by a series of bitter civil wars being fought for control of the kingdom after the death of its last great ruler, Ashurbanipal. Nabo-Polassar allied Babylonia with the Medes, Persians, Cimmerians and Scythians. A weakened Assyria could not withstand this added pressure, and in 612 BC, Nineveh, the capital of Assyria, fell. The entire city, was sacked.

Later, Nebuchadnezzar II (Nabopolassar's son) inherited a proportion of the former Assyrian empire for Babylonia. He added territory to Babylonia and undertook much building work in the city.

The Seleucids were succeeded by the Parthian Empire in the 3rd century BC. At the beginning of the 2nd century AD, the Romans, led by emperor Trajan, invaded Parthia and conquered Mesopotamia, making it an imperial province. It was returned to the Parthians shortly after by Trajan's successor, Hadrian.

Christianity entered Mesopotamia in the 1st century AD, and Assyria in particular became the center of Eastern Rite Christianity and the Syriac literary tradition. Native Mesopotamian Religion began to die out during this period, although temples were still being dedicated to the Assyrian national god Ashur in his home city as late as the 4th century.[9]

In the 3rd century AD, the Parthians were in turn succeeded by the Sassanid dynasty, which ruled Mesopotamia until the 7th century Islamic caliphate rule, after which point Assyria (Assuristan) was dissolved. The Sassanids conquered the independent Neo-Assyrian states of Adiabene, Osroene, Hatra and finally Assur during the 3rd century AD.

In the mid-6th century the Persian Empire under the Sassanid dynasty was divided by Khosrow I into four quarters, of which the western one, called Khvārvarān, included most of modern Iraq, and subdivided to provinces of Mishān, Asuristān (Assyria), Adiabene (which was for a time an independent Assyrian state) and Lower Media. The term Iraq is widely used in the medieval Arabic sources for the area in the center and south of the modern republic as a geographic rather than a political term, implying no greater precision of boundaries than the term "Mesopotamia" or, indeed, many of the names of modern states before the 20th century.

The area of modern Iraq north of Tikrit was known in Arab Muslim times as Al-Jazirah, which means "The Island" and refers to the "island" between the Tigris and Euphrates rivers. To the south of Mesopotamia lay the Arabian deserts, inhabited largely by ethnic Arab tribesmen who acknowledged the overlordship of the Sassanian Emperors, as they had to the Assyrian, Babylonian, Achaemenid, Seleucid and Parthian emperors before them.

Until 602, the desert frontier of the Persian Empire had been guarded by the ArabLakhmid kings of Al-Hirah, who were themselves Arabs but who ruled a settled buffer state subject to Persia. In that year ShahanshahKhosrow II Aparviz (Persian خسرو پرويز) abolished the Lakhmid kingdom and laid the frontier open to nomad incursions. Farther north, the western quarter was bounded by the Byzantine Empire. The frontier more or less followed the modern Syria-Iraq border and continued northward into modern Turkey, leaving Nisibis (modern Nusaybin) as the Sassanian frontier fortress while the Byzantines held Dara and the nearby Assyrian populated Amida (modern Diyarbakır).

The first organised conflict between local Arab tribes and Persian forces seems to have been in 634, when the Arabs were defeated at the Battle of the Bridge. There was a force of some 5,000 Muslims under Abū `Ubayd ath-Thaqafī, which was routed by the Persians. This was followed by Khalid ibn al-Walid's successful campaign which saw all of Iraq come under Arab rule within a year, with the exception of the Persian Empire's capital, Ctesiphon. Around 636, a larger Arab Muslim force under Sa`d ibn Abī Waqqās defeated the main Persian army at the Battle of al-Qādisiyyah and moved on to capture the Persian capital of Ctesiphon. By the end of 638, the Muslims had conquered all of the Western Sassanid provinces (including modern Iraq), and the last Sassanid Emperor, Yazdegerd III, had fled to central and then northern Persia, where he was killed in 651.

The Islamic invasion was followed by immigration from the Arabian Peninsula. Though this was by no means the first of such emigrations, as migration from the Arabian peninsula to the Fertile Crescent has been a pattern of human behaviour since antiquity, the Islamic expansions constituted the largest of the Semitic expansions in history. These new arrivals did not disperse and settle throughout the country; instead they established two new garrison cities, at al-Kūfah, near ancient Babylon, and at Basrah in the south, while the north remained largely Assyrian and Christian in character.

During the late 14th and early 15th centuries, the Black Sheep Turkmen ruled the area now known as Iraq. In 1466, the White Sheep Turkmen defeated the Black Sheep and took control. In the 16th century, most of the territory of present-day Iraq came under the control of Ottoman Empire as the pashalik of Baghdad. Throughout most of the period of Ottoman rule (1533-1918) the territory of present-day Iraq was a battle zone between the rival regional empires and tribal alliances. Iraq was divided into three vilayets:

The Safavid dynasty of Iran briefly asserted their hegemony over Iraq in the periods of 1508-1533 and 1622-1638. During the years 1747-1831 Iraq was ruled by the Mamluk officers of Georgian origin who succeeded in obtaining autonomy from the Ottoman Empire, suppressed tribal revolts, curbed the power of the Janissaries, restored order and introduced a program of modernization of economy and military. In 1831, the Ottomans managed to overthrow the Mamluk regime and again imposed their direct control over Iraq.[18]

Ottoman rule over Iraq lasted until World War I, when the Ottomans sided with Germany and the Central Powers. In the Mesopotamian campaign against the Central Powers, British forces invaded the country and suffered a defeat at the hands of the Turkish army during the Siege of Kut (1915–16). However the British finally won in the Mesopotamian Campaign with the capture of Baghdad in March 1917. During the war the British employed the help of a number of Assyrian, Armenian and Arab tribes against the Ottomans, who in turn employed the Kurds as allies. After the war the Ottoman Empire was divided up, and the British Mandate of Mesopotamia was established by League of Nations mandate. Britain imposed a Hāshimite monarchy on Iraq and defined the territorial limits of Iraq without taking into account the politics of the different ethnic and religious groups in the country, in particular those of the Kurds and the ChristianAssyrians to the north. During the British occupation, the Shi'ites and Kurds fought for independence, and the British employed Assyrian Levies to help quell these insurrections. Iraq also became an oligarchy government at this time.

Although the monarch Faisal I of Iraq was legitimized and proclaimed King by a plebiscite in 1921, independence was achieved in 1932, when the British Mandate officially ended.

Establishment of Arab Sunni domination in Iraq was followed by Assyrian, Yazidi and Shi'a unrests, which were all brutally suppressed. In 1936, the first military coup took place in the Kingdom of Iraq, as Bakr Sidqi succeeded in replacing the acting Prime Minister with his associate. Multiple coups followed in a period of political instability, peaking in 1941.

In 1945, Iraq joined the United Nations and became a founding member of the Arab League. At the same time, the Kurdish leader Mustafa Barzani led a rebellion against the central government in Baghdad. After the failure of the uprising Barzani and his followers fled to the Soviet Union.

In 1948, massive violent protests, known as the Al-Wathbah uprising broke out across Baghdad as a popular demand against the government treaty with the British, and with communist part support. More protests continued in spring, but were interrupted in May, with the marshal law, when Iraq entered the failed 1948 Arab-Israeli War along with other members of the Arab League.

In February 1958, King Hussein of Jordan and `Abd al-Ilāh proposed a union of Hāshimite monarchies to counter the recently formed Egyptian-Syrian union. The prime minister Nuri as-Said wanted Kuwait to be part of the proposed Arab-Hāshimite Union. Shaykh `Abd-Allāh as-Salīm, the ruler of Kuwait, was invited to Baghdad to discuss Kuwait's future. This policy brought the government of Iraq into direct conflict with Britain, which did not want to grant independence to Kuwait. At that point, the monarchy found itself completely isolated. Nuri as-Said was able to contain the rising discontent only by resorting to even greater political oppression.

In 1961, Kuwait gained independence from Britain and Iraq claimed sovereignty over Kuwait. A period of considerable instability followed. The same year, Mustafa Barzani, who had been invited to return to Iraq by Qasim three years earlier, began engaging Iraqi government forces and establishing Kurdish control in the north in what was the beginning of the First Kurdish Iraqi War.

Qāsim was assassinated in February 1963, when the Ba'ath Partytook power under the leadership of General Ahmed Hassan al-Bakr (prime minister) and Colonel Abdul Salam Arif (president). In June 1963, Syria, which meanwhile had also fell under Ba'athist rule, took part in the Iraqi military campaign against the Kurds by providing aircraft, armoured vehicles and a force of 6,000 soldiers. Several months later, `Abd as-Salam Muhammad `Arif led a successful coup against the Ba'ath government. Arif declared a ceasefire in February 1964 which provoked a split among Kurdish urban radicals on one hand and Peshmerga (Freedom fighters) forces led by Barzani on the other.

On April 13, 1966, President Abdul Salam Arif died in a helicopter crash and was succeeded by his brother, General Abdul Rahman Arif. Following the unexpected death of Arif, whereupon he was replaced by his brother, Abdul Rahman Arif, the Iraqi government launched a last-ditch effort to defeat the Kurds. This campaign failed in May 1966, when Barzani forces thoroughly defeated the Iraqi Army at the Battle of Mount Handrin, near Rawanduz. Following the Six Day War of 1967, the Ba'ath Party felt strong enough to retake power in 1968. Ahmed Hassan al-Bakr became president and chairman of the Revolutionary Command Council (RCC). The Ba'ath government started a campaign to end the Kurdish insurrection, which stalled in 1969. This can be partly attributed to the internal power struggle in Baghdad and also tensions with Iran. Moreover, the Soviet Union pressured the Iraqis to come to terms with Barzani. The war ended with more than 100,000 mortal casualties, with little achievements to both Kurdish rebels and the Iraqi government.

In the aftermath of the First Kurdish Iraqi War, a peace plan was announced in March 1970 and provided for broader Kurdish autonomy. The plan also gave Kurds representation in government bodies, to be implemented in four years.[20] Despite this, the Iraqi government embarked on an Arabization program in the oil rich regions of Kirkuk and Khanaqin in the same period.[21] In the following years, Baghdad government overcame its internal divisions and concluded a treaty of friendship with the Soviet Union in April 1972 and ended its isolation within the Arab world. On the other hand, Kurds remained dependent on the Iranian military support and could do little to strengthen their forces. By 1974 the situation in the north escalated again into the Second Kurdish Iraqi War, to last until 1975.

Territorial disputes with Iran led to an inconclusive and costly eight-year war, the Iran–Iraq War (1980–1988, termed Qādisiyyat-Saddām – 'Saddam's Qādisiyyah'), which devastated the economy. Iraq declared victory in 1988 but actually achieved a weary return to the status quo ante bellum, meaning both sides retained their original borders.

The war began when Iraq invaded Iran, launching a simultaneous invasion by air and land into Iranian territory on 22 September 1980, following a long history of border disputes, and fears of Shia insurgency among Iraq's long-suppressed Shia majority influenced by the Iranian Revolution. Iraq was also aiming to replace Iran as the dominant Persian Gulfstate. The United States supported Saddam Hussein in the war against Iran.[22] Although Iraq hoped to take advantage of the revolutionary chaos in Iran and attacked without formal warning, they made only limited progress into Iran and within several months were repelled by the Iranians who regained virtually all lost territory by June 1982. For the next six years, Iran was on the offensive.[23] Despite calls for a ceasefire by the United Nations Security Council, hostilities continued until 20 August 1988. The war finally ended with a United Nations brokered ceasefire in the form of United Nations Security Council Resolution 598, which was accepted by both sides. It took several weeks for the Iranian armed forces to evacuate Iraqi territory to honor pre-war international borders between the two nations (see 1975 Algiers Agreement). The last prisoners of war were exchanged in 2003.[23][24]

Saddam Hussain during Iran-Iraq War, which cost an estimated 1 million casualties

The war came at a great cost in lives and economic damage—half a million Iraqi and Iranian soldiers as well as civilians are believed to have died in the war with many more injured—but it brought neither reparations nor change in borders. The conflict is often compared to World War I,[25] in that the tactics used closely mirrored those of that conflict, including large scale trench warfare, manned machine-gun posts, bayonet charges, use of barbed wire across trenches, human wave attacks across no-man's land, and extensive use of chemical weapons such as mustard gas by the Iraqi government against Iranian troops and civilians as well as Iraqi Kurds. At the time, the UN Security Council issued statements that "chemical weapons had been used in the war." However, in these UN statements it was never made clear that it was only Iraq that was using chemical weapons, so it has been said that "the international community remained silent as Iraq used weapons of mass destruction against Iranian as well as Iraqi Kurds" and it is believed.

A long-standing territorial dispute was the ostensible reason for Iraq's invasion of Kuwait in 1990. In November 1990, the UN Security Council adopted Resolution 678, permitting member states to use all necessary means, authorizing military action against the Iraqi forces occupying Kuwait and demanded a complete withdrawal by January 15, 1991. When Saddam Hussein failed to comply with this demand, the Persian Gulf War (Operation "Desert Storm") ensued on January 17, 1991. Probably as many as 30,000 Iraqi soldiers and a few thousand civilians were killed.[citation needed]

In March 1991 revolts in the Shia-dominated southern Iraq started involving demoralized Iraqi Army troops and the anti-government Shia parties. Another wave of insurgency broke out shortly afterwards in the Kurdish populated northern Iraq (see 1991 uprisings in Iraq). Although they presented a serious threat to the Iraqi Ba'ath Party regime, Saddam Hussein managed to suppress the rebellions with massive and indiscriminate force and maintained power. They were ruthlessly crushed by the loyalist forces spearheaded by the Iraqi Republican Guard and the population was successfully terrorized. During the few weeks of unrest tens of thousands of people were killed. Many more died during the following months, while nearly two million Iraqis fled for their lives. In the aftermath, the government intensified the forced relocating of Marsh Arabs and the draining of the Iraqi marshlands, while the Coalition established the Iraqi no-fly zones.

On 6 August 1990, after the Iraqi invasion of Kuwait, the U.N. Security Council adopted Resolution 661 which imposed economic sanctions on Iraq, providing for a full trade embargo, excluding medical supplies, food and other items of humanitarian necessity, these to be determined by the Security Council sanctions committee. After the end of the Gulf War and after the Iraqi withdrawal from Kuwait, the sanctions were linked to removal of weapons of mass destruction by Resolution 687[2]. From 1991 until 2003 Iraq underwent hyperinflation, increased poverty and malnutrition. To varying degrees, the effects of government policy, the aftermath of Gulf War and the sanctions regime have been blamed for these conditions.

During the late 1990s, the U.N. considered relaxing the sanctions imposed because of the hardships suffered by ordinary Iraqis. Studies dispute the number of people who died in south and central Iraq during the years of the sanctions. It is also disputed whether any extra hardship was caused by the sanctions or whether this was the result of other factors.[26][27][28] However, an oil for food program was established in 1996 to ease the effects of sanctions.

Iraqi cooperation with UN weapons inspection teams was questioned on several occasions during the 1990s. UNSCOM chief weapons inspector Richard Butler withdrew his team from Iraq in November 1998 because of Iraq's lack of cooperation. The team returned in December.[29] Butler prepared a report for the UN Security Council afterwards in which he expressed dissatisfaction with the level of compliance [3]. The same month, US President Bill Clinton authorized air strikes on government targets and military facilities. Air strikes against military facilities and alleged WMD sites continued into 2002.

After the terrorist attacks on New York and Washington in the United States in 2001 were linked to the group formed by the multi-millionaire Saudi Osama bin Laden, American foreign policy began to call for the removal of the Ba'ath government in Iraq. Conservative think-tanks in Washington had for years been urging regime change in Baghdad, but until the Iraq Liberation Act of 1998, official US policy was to simply keep Iraq complying with UN sanctions. The Iraq Liberation Act, codified regime change in Iraq as the official policy of the United States government. It was passed 99-0 by the United States Senate in 1998.

The US urged the United Nations to take military action against Iraq. American president George W. Bush stated that Saddām had repeatedly violated 16 UN Security Council resolutions. The Iraqi government rejected Bush's assertions. A team of U.N. inspectors, led by Swedish diplomat Hans Blix was admitted, into the country; their final report stated that Iraqis capability in producing "weapons of mass destruction" was not significantly different from 1992 when the country dismantled the bulk of their remaining arsenals under terms of the ceasefire agreement with U.N. forces, but did not completely rule out the possibility that Saddam still had Weapons of Mass Destruction. The United States and the United Kingdom charged that Iraq was hiding Weapons and opposed the team's requests for more time to further investigate the matter. Resolution 1441 was passed unanimously by the UN Security Council on November 8, 2002, offering Iraq "a final opportunity to comply with its disarmament obligations" that had been set out in several previous UN resolutions, threatening "serious consequences" if the obligations were not fulfilled. The UN Security Council did not issue a resolution authorizing the use of force against Iraq.

In 2003, after the American and British invasion, Iraq was occupied by Coalition forces. On May 23, 2003, the UN Security Council unanimously approved a resolution lifting all economic sanctions against Iraq.

As the country struggled to rebuild after three wars and a decade of sanctions, it was plagued by violence between a growing Iraqi insurgency and occupation forces. Saddam Hussein, who vanished in April, was captured on December 13, 2003.

Jay Garner was appointed Interim Civil Administrator with three deputies, including Tim Cross. Garner was replaced in May 2003 by L. Paul Bremer, who was himself replaced by John Negroponte on April 19, 2004 who left Iraq in 2005. Negroponte was the last US interim administrator.

Terrorism emerged as a threat to Iraq's people not long after the invasion of 2003. Al Qaeda now has a presence in the country, in the form of several terrorist groups formerly led by Abu Musab Al Zarqawi. Al-Zarqawi was a Jordanian militant Islamist who ran a militant training camp in Afghanistan. He became known after going to Iraq and being responsible for a series of bombings, beheadings and attacks during the Iraq war. Al-zarqawi was killed on June 7, 2006. Many foreign fighters and former Ba'ath Party officials have also joined the insurgency, which is mainly aimed at attacking American forces and Iraqis who work with them. The most dangerous insurgent area is the Sunni Triangle, a mostly Sunni-Muslim area just north of Baghdad.

By the end of 2006 violence continued as the new Iraqi Government struggled to extend complete security within Iraq.

U.S. and Coalition forces remained in Iraq. An increasingly disturbing trend had arisen - sectarian fighting. This new phase of conflict was waged predominately along religious sectarian lines. Fighting was primarily between the majority Shia and the minority Sunni. But there were reports of infighting as well. Reported acts of violence conducted by an uneasy tapestry of insurgents steadily increased by the end of 2006. According to official US figures, these attacks were overwhelming directed at American forces.[30] Also, criminal elements within Iraq's society seemed to perpetuate violence for their own means and ambitions. Further, Islamic Jihadist - of which Al Qaeda in Iraq is a member - continued to use terror and extreme acts of violence promarily against Shia civilians to advance their religious and political agenda(s). The aims of these attacks were not completely clear, but it was argued in 2006/7 that these attacks were aimed at fomenting civil conflict within Iraq to destroy the legitimacy of the newly elected Iraqi government and create an unsustainable position for the U.S. forces within Iraq. The most widely reported evidence of this argument stemmed from the 23 February 2006 attack on the Al Askari Mosque in Samarra, one of Shi'ite Islam's holiest sites. Analysis of the attack suggested that the Mujahideen Shura Council and Al-Qaeda in Iraq were responsible, and that the motivation was to provoke further violence by outraging the Shia population. [4] The Mujahideen Shura Council was said to have been headed by Abdullah Rashid al-Baghdadi.[31] In mid-October 2006, a statement was released, stating that the Mujahideen Shura Council had been disbanded and was replaced by the "Islamic State of Iraq". It was formed to resist efforts by the U.S. and Iraqi authorities to win over Sunni supporters of the insurgency.

In response to attacks like the one against the Askari Mosque, violence escalated. Shia militias, some of whom were associated with elements in the Iraq government, reacted with violence against Sunnis. Additionally, the militias, it appeared in late 2006, had the capability to act outside the scope of government. As a result these powerful militias, it seemed as of late 2006, were leading reprisal acts of violence against the Sunni minority. A cycle of violence thus ensued whereby Sunni insurgent attacks were followed reprisals by Shiite militias- often in the form of Shi'ite death squads that sought out and killed Sunnis. Many commentators on the Iraq War began, by the end of 2006, to refer to this violent escalation as a civil war.

Following a surge in U.S. troops in 2007 and 2008, violence in Iraq began to decrease. The war was declared formally over in December 2011. The U.S. ended their main military presence in 2011.[32]